Vanishing images and error 400 previews

Hi everyone, I am a newbie to WP migrating from joomla, please be patient with me.

I am rebuilding my site with a sub directory bfore moving it over. I am copying pages one by one from the live site. I am finding that I can draft a post (or page) fine and the preview works and the images attach fine when I upload them. The minute I hit publish the images vanish and the preview function and view function tabs come up with error 400 pages. I use firefox, have cleared my cache but problem still persists.